I triggered a build against my circle ci integration, through phab's build step interface. Let's see how it goes: https://circleci.com/gh/alpmestan/ghc/15 (previously, it'd just blow up, trying to build and run things with -j9 on a 2 core box with 4GB of RAM).

It looks like switching to the ghc-diffs repo you created as a "staging" one for the Circle CI builds did the trick. Not sure how important the core detection logic was in making this work, but I suppose it is anyway better not to just blindly run with -j9.